This invention relates generally to transducers suitable for forming fiber optic sensors. This invention relates particularly to fiber optic transducers that include a coil of optical fiber wound on a mandrel and including a Bragg grating formed in the optical fiber. Still more particularly, this invention relates to a transducer mandrel with an attached collar for mounting a fiber Bragg grating (FBG) and having a smooth transition from a fiber optic sensor coil to the FBG.
A fiber optic sensor typically includes a transducer comprising a mandrel that supports a coil of optical fiber. Depending upon the configuration of the mandrel, a fiber optic transducer may be made to be sensitive to changes in temperature, pressure or sound intensity. In a sensor array having a plurality of such transducers, an FBG typically is mounted between the optical fiber coils on the mandrels. The purpose of the FBG is to reflect an optical signal of a selected wavelength back through the optical fiber to a detector and to transmit optical signals of other wavelength to subsequent transducers in the array. Typically the FBG is wound on a grating collar that is slid over an end of the corresponding sensor mandrel. It has been found that supporting the grating collar on the sensor mandrel causes a differential strain on the grating collar, which in turn causes unwanted changes in the optical characteristics of the FBG.